The present invention relates generally to the field of cannulas used to provide a conduit and channel through the skin of a patient for performing internal medical procedures. More specifically, the invention relates to such cannulas, both regular and insufflation types, having a valve mechanism to seal off the conduit to prevent fluids or gases from escaping out the exterior end of the cannula. The valve mechanism is of an improved construction and assembly, whereby the integrity of the valve seal is maintained over repeated uses and replacement of the sealing gasket within the valve mechanism is a simple procedure.
Cannulas in combination with trocars are well known in the art. The cannula and trocar combination is used to penetrate the skin of a patient so that medical procedures may be performed internally without recourse to a relatively large incision, the trocar creating only a small puncture site. The internal trocar is removed after penetration and the cannula provides the conduit through which instruments may be inserted and manipulated, or if the cannula is of the insufflation type, gases inserted to expand the internal cavity.
Valved cannulas are well known in the art. For example, U.S. Pat. No. 4,943,280 to Lander, U.S. Pat. No. 4,233,982 to Bauer et al., U.S. Pat. No. 4,245,635 to Kontos and U.S. Pat. No. 4,631,051 to Harris all show valved cannulas. The known devices all suffer from various drawbacks and problems which are not present in the cannula of the invention. To provide a gas-tight and fluid-tight seal, a typical valve mechanism comprises a pivoting plug in combination with a resilient gasket, the plug being adapted to be pushed open by the inserted instruments and the gasket forming a seal with either the plug or the inserted instrument. The integrity of the seal depends upon the gasket continuing to perform its function over many repeated usages. The known devices fall into two main categories--those with an exposed gasket, as in Bauer et al., and those with intricately shaped gaskets, as in Lander.
A cannula is typically used with pointed or hooked instruments, and it is important that the sharp portions of the instruments not contact the sealing gasket. Some cannulas have the gasket positioned on the pivoting plug member. This is a poor design, in that it exposes the gasket to contact with the trocar or other instruments every time they are inserted to force open the valve, since the gasket is not stationary about the central axis of the cannula shaft. This often results in slicing or tearing of the gasket. Using a fixed gasket alleviates this problem, but the current assemblies require complicated gaskets which can wear out from fatigue or have large exposed surfaces allowing shifting or stretching of the gasket.
The valve mechanism of the invention solves these problems by providing a simple annular gasket which is maintained in a fixed position relative to the central a is. The retaining means for the gasket provide for an improved seal with the valve plug and allow for easy removal and replacement of the gasket when necessary.